Blasting detonator



IL an' Dec. 13, 1955 c. o. DAVIS ETAL 2,726,602

BLASTING DETONATOR Filed July l, 1952 INVENTORS' Clyde Oliver DavisATTORNEYS United States Patent O BLASTING DETONATR Clyde Oliver Davis,Wenonah, N. J., Harold Arthur Lewis,

Wilmington, Del., and George Adalbert Noddin, Clarksboro, N. J.,assigner-s to E. I. du Pont de Nemours e2 Company, Wilmington, Dei., acorporation of Delaware Application July 1, 1952, Serial No. 296,546

Claims. (Ci. 162-29) This invention relates to a novel detonator for usein blasting under liquid confinement and particularly to such adetonator which is fired without attached initiating means.

This application is a continuation-impart of our copending applicationSerial No. 792,202, led December i7, 1947 (now abandoned).

Underwater blasting operations are required for such purposes as thedeepening of harbors and channels, the removal of rock obstructions, thedestruction of sunken objects, and the like. In such work, it iscustomary to prepare the required number of boreholes spaced at suitabledistances apart and to load high-strength explosive into each of saidboreholes. Heretofore in such blasting, it has been necessary to followone of two procedures, each of kwhich involved serious disadvantages.One method consisted in spacing the boreholes suiciently close together,loading each of the holes with explosive, initiating one of the chargesby means of an electric blasting cap, and bringing about explosion ofthe other charges by propagation from hole to hole. The disadvantage ofsuch a method was that the use of explosives of a high degree ofsensitivity was required. As a matter of fact, it has been customary insuch work to employ 60% straight dynamite, high-strength gelatin, orhighstrength gelatine primed with 60% straight. The use of highexplosives of such an order or sensitiveness is u ndesirable and undulyhazardous for large-scale rock blasting operations where a certainamount of rough handling is necessary. Furthermore, premature explosionson drill barges with consequent loss of life have occurred with thesehighly sensitive explosives.

A second method practiced heretofore has allowed the use of many typesof cap-sensitive explosives but has necessitated the insertion of atleast one electric blasting cap into each borehole charge. This has notonly been wasteful in its requirements of relatively expensive electricblasting caps but has introduced complications be- 1 cause of thepresence of the many cap wires of considerable length, which couldreadily become tangled or fouled by material oating on or submerged inthe water, by passing vessels, etc. A distinct hazard is involved alsoin the event of electrical storms, not necessarily in the immediatevicinity, which in a number of'cases have brought about the explosion ofunderwater charges with emergent cap wires.

In view of the disadvantages present in previous procedures forsubmarine blasting, where a plurality of explosive charges is to be red,it will be apparent that a method that allows the use of relativelyinsensitive explosives without requiring-electric blasting caps Wired toeach charge will represent a highly desirable advance.

An object of the present invention is a novel method of carrying outblastingoperations beneath the surface Aof or in contact with a denseliquid medium and particularly for .underwater blasting. A furtherobject is such a method permitting the employment of relativelyinsensitive blasting explosives and not requiring electric blast-2,726,602 Patented Dec. 13, 1955 ing caps and their wires for thevarious charges. A still further object is a method for submarineblasting employing a novelrtype of detonator. A further object is adetonator adapted for underwater blasting characterized by simplicity ofconstruction and high reliability of action, free from electrical ordame-action means of detonation, and adapted to be initiated under theeffect of suddenly applied external pressure. Additional objects will bedisclosed as the invention is described at greater length hereinafter. K

We have found that the foregoing objects are accomplished when we carryout submarine blasting operations by a method comprising introducing aplurality of explosive charges into the desired subsurface blastingpositions; locating at least one of the novel detonators adjacent toeach of the explosive charges and in detonating relationship therewith,said detonator being free from electrical tiring arrangements andadapted to become initiated as a result of the sudden collapse of theshell Walls under the eect of pressure from the explosion of a nearbycharge; locating an explosive priming charge in suitable proximity tosaid pressure-responsive detonator; bringing about the explosion of saidpriming charge; and thereby causing the collapse of the shells of thepressureresponsive detonators, the initiation of the respectivedetonator charges and the detonation of the main explosive chargesadjacent thereto. The detonators adapted to collapse under pressure, asdescribed, will contain in a completely sealed tubular metal shell ofdefinite minimum strength a high-density, high-velocity base charge, acompressed intermediate charge, and, in a portion of the shell inigniting relationship with the intermediate charge, a

loose, granular explosive composition of the ignition type, whichcomposition does not fill the said portion of the shell. The ignitioncharge will become ignited as a result of the impact of the collapsingwalls. The high-velocity, high-density detonating explosive base chargewithin the cap will be brought to explosion by the loose charge by wayof the compressed intermediate charge.

The invention will be illustrated more clearly by reference to theattached drawing, in which Figure l is a longitudinal section of apressure-responsive detonator according, to the invention. Figure 2 is asimilar view of such a pressure-responsive detonator of modified con-vstruction. Figure 3 represents a delay detonator according to theinvention. Figure 4 is a detonator similar to' that of Figure l exceptthat different sealing means are employed. Figure 5 is a cross-sectionof an empty shell after collapse. Figures 6, 7, and 8 are diagrammaticviews of diterent arrangements of explosive charges under liquid media,adapted to employ the'principle of the invention.

Withl special reference to Figure l, 1 is a metal shell of suchdimensions and wall thickness as to permit the shell to withstand staticpressures of more than 2000 lb./sq. in. Within this shell at its base orinitially closed end is a compressed charge 2 of pentaerythritoltetranitrate or other high-velocity explosive suitable for use as basecharge. The primer charge 3 vis a pressed composition more-readilyignitible by dame than the base charge, and a suitable materialcomprises a lead azide composition. This charge 3 is shown in thedrawing as embedded in a preformed cavity in the base charge forpurposes of protection. The shell is closed at its upper end by aclosely fitting rubber plug 4, which has been crimped into completelywater-tight relationship with the shell wall. Between the rubber plugand the primer charge is a space in the shell into whichhas beenintroduced so as not to fill the space a loose, granular charge of anexplosive com# veloped by the detonation of a nearby explosive primingcharge. A suitable composition for this friction-ignitible charge is ablend of mercury fulminate and potassium chlorate in a 90/ l0 ratio.

vIn Figure 2 a detonator of similar construction is shown, with theexception that a Zig-zag metal wire 6 has been secured in predeterminedposition within the rubber plug 4 so that the end projects beyond thesurface of said plug, the wire extending into the space containing theignition-type composition 5, which is adapted to function in the mannerdescribed for Figure 1. A suitable cornposition is a 50/ 25/ 25 blend ofsmokeless powder, a complex salt of lead nitrate with the bis basic leadsalt of 4,-dinitro-ortho-cresol, and potassium chlorate. Although thepresence of the bent wire is not essential to the invention, itincreases the frictional etfect on collapse of the shell walls in theunsupported portion and allows the utilization effectively of a lesssensitive explosive cornposition in this portion of the detonator.

Figure 3 shows the construction of a pressure-responsive detonator ofthe delay type, in accordance with the invention, adapted to becomeinitiated by the pressure from a nearby explosion and to bring about thedetonation of its explosive charge after a predetermined time intervalfollowing the burning of the initial charge. In this figure, 1designates ,a metal shell containing at its base a pressed charge 2 of asuitable high-velocity explosive such as tetryl, with a primer charge 3of pressed lead azide in detonating relationship with the base chargeand loaded into -a formed cavity in said base charge. Above the primercharge and in ignition relationship therewith is a metal carrier 7having a centrally located longitudinal bore, into which is pressed aslow-burning charge 8 controlled to burn at a predetermined speed. Thisslowburn-ing charge should desirably be one that burns withoutsubstantial evolution of gas so that no great pressure will be developedto burst the shell walls duringthe delay interval. A suitablecomposition will be, for example, a mixture of metallic selenium andbarium peroxide. The upper lend yof the metal shell is closed by meansof a water-tight rubber plug 4 crimped into position. Between thisrubber plug and the delay carrier 7 is a' chamber into which has beenintroduced so as not to till the chamber entirely a loosely-packedcharge of a composition of the ignition type adapted to become ignitedwhen the shell walls at this position collapse suddenly under the effectof the :pressure from anearby exploding charge.

Figure 4 shows a pressure-responsive detonator simiiar to that vofFigure 1, except that the sealing is accomplished in another manner.Whereas :in Figure l, a closure that is kliquid-tight under pressure isaccomplished by 'means of the yclosed .end of metal shell 1 and therubber plug 4 inserted and crimped in the previously open end of shell1, i-n Figure 4 the tubular shell l is initially open at both ends andis sealed at each of these ends by a metal plug 9 which'its `:exactlyinto the tubular shell 1 and is provided with a head of the samediameter yas the outer diameter of the .shell and with a lgroove belowthe head into which is introduced a sealing composition 10. Thestructure of Figure 4 is particularly vapplicable to relativelyVthickivalled detonators.

Figure 5 is across-section ofthe chamber for containing' theignition-type charge as 4it ordinarily appears after'it has beencollapsed by high static kpressures in the absence of .an ignitioncharge. (When the shell collapses in the presence ofthe ignition charge,it is, of course, destroyed.) It will be seen .that collapse hasoccurred from all sides and .that the cross-section has assumed apleated form.

Although this `is the usual manner of collapse of the shells,

the detonators will function if vcollapse occurs in other manners, as byflattening of the tubular wall of the collapse.chamber, for example.

In Figure 6 is shown an assembly for underwater .blasting using thepressure-responsive detonator of the present invention. In this figure,11 represents the surface of a body of water, beneath which, andconfined by said body, have been placed explosive charges 13 and 14, inboreholes in the rock bottom 12. Inserted in these charges arepressure-responsive detonators 1S and 16, of the type described inFigures l, 2, and 4. An explosive charge 17 has been lowered into aposition in proximity to detonators 15 and 16, and an electric blastingcap 18 is in detonating relationship with this charge, having insulatedcap wires 19. When ready for the blast, the cap wires are thrown intocircuit with a source of electric current (not shown) and the charge istired. The pressure resulting from the detonation of charge 17 bringsabout the sudden inward collapse of the walls of pressure-responsivedetonators 15 and 16, with consequent detonation of the charges 13 and14. In this figure, two explosive charges have been shown containinginserted pressure-responsive detonators and in position to be explodedunder the intluence otpressure.

Figure 7 shows another and a preferred assembly of charges forunderwater blasting employing the pressureresponsive detonator of thepresent invention. In this figure, six explosive charges 21--26, areshown loaded into their respective boreholes in the rock bottom 12,spaced from one another at reasonably short distances. Into charge 21,an electric blasting cap 27 has been inserted, having insulated capwires 33. Spaced from charge 21 are the successive explosive charges 22,23, 24, 25, and 26, into each of which has been introduced anon-electric closed detonator of the type described in Figures 1, 2, and4, these detonators being designated by 28 29, 30, 31, and 32,respectively. At the time of tiring, the wires from the cap in explosivecharge 21 are connected with a source of tiring current, and electricblasting cap 27 and charge 21 are brought tol detonation. The adjacentexplosive charges 22--26 are not suiciently sensitive to propagation tobe detonated sympathetically by the rst charge 21, but the resultinghydrostatic pressure generated by detonation of charge 21 causes thecollapse of the walls of detonator 28 and the detonation of this and itscharge 22 and the subsequent successive detonation of charges 23-26 bymeans of the inserted pressureresponsive detonators. It will beunderstood that, in the illustration of the invention according toFigure 7, the explosive charges in the dilerent boreholes may consist ofsingle cartridges in each hole or a column or group of cartridges. Wherea vnumber of cartridges are present in each hole, a singlepressure-responsive detonator in the top cartridge may be suicient, theexplosion propagating from one cartridge to another, or, if desired,pressure-responsive detonators may be present in all or in any chosennumber of the cartridges, depending on the sensiti-Veness of theexplosive and the continuity of the column.

Figure 8 is a longitudinal sectional view of the bottom of an oil wellshowing relative positions therein of a series of explosive chargesprovided With pressure-responsive detonators in accordance with thisinvention. There -is shown the bottom portion of a well 40 filled withliquid 41. -In Vthe well, containers 42, 43, 44, and 45 of ,any

uitable form which enclose explosive charges of any suitable, relativelyinsensitive type, which charges have Ainserted thereinpressure-responsive detonators 46, 47, 48, and 49, are spaced from oneanother by lengths of rigid tubing 50, 51, and 52, or other conventionalmeans. When an explosion :is caused in the vicinity of the uppermostcharge 45 by an oil-well time bomb 53 suspended above the uppermostcharge 45 or by another usual initiating charge vfor oil-Well blastingsuch as a percussion-initiated squib, for example, thepressure-responsive detonators 46, 47, 4.8 and 49 inserted in theexplosive charges in containers 42, 43, 44, 145 all are collapsed 'bythe increase in 'pressurein the well in their vicinity caused bythe ex-The method described in the foregoing will be applicable inblastingoperations beneath the surface of a `dense liquid medium, andparticularly in submarine blasting, for the deepening of harbors andchannels, the removal of rock obstructions, the destruction anddisintegration of sunken objects, shaft sinking, and the like. It hasother sub-liquid applications, however, for example in oil-well shootingand in various uses of `explosives in the oil-production industry. Bythe words dense liquid medium we intend to include all liquids andsuspensions of solids in liquids, e. g. mud, wet sand, and allsolidcontaining mixtures that may be caused to flow under pressure. Themethod is advantageous, for example, in ditch blasting in thatexplosives may be used which are more insensitive, and hence safer tohandle, than the usual straight dynamites which have heretofore beenrequired to permit propagation from cartridge to cartridge bysympathetic detonation through a wet soil medium.

With respect to explosive compositions for use in pressure-responsivedetonators, the usual requirements will hold for base and intermediatecharges. As base charges, a high-velocity explosive should Ybe employedthat accelerates rapidly toits maximum velocity when properly primed.This charge should be compressed to high density, e. g. around 1.6g./cc., and suitable `materials for useare pentaerythritol tetranitrate,tetryl, cyclotrimethylenetrinitramine, and the like.` Such highlycompressed charges are not sucient readily ignitible by flame, and anintermediate or primary charge is customarily introduced, for example,mercury fulminate and its blends with chlorate, lead azide,nitromannitol, diazodinitrophenol, etc. While such a charge has beenshown in the drawings as enclosed in a cavity in the base charge, thisprimary charge may occupy for a short length, around 1A; inch forexample, the entire shell column. The intermediate or priming charge islikewise loaded under compression, for example Vabout 4000 lb./ sq. in.Hence, both the base charge and the primary charge are so consolidatedas to remain xed in position within the shell and to prevent thecollapse in that portion of the shell which they occupy.

By explosive composition of the ingnition type is meant an explosivecompound or mixture commonly used in the explosive art as an ignitioncomposition, i. e. a compound or mixture susceptible when in loose,uncompacted condition to ignition by an incandescent wire, such as by anelectrically heated small-diameter platinum or Nichrome bridge wire ascommonly used in the art. Examples of such compositions of the ignitiontype include mercury fulminate or its mixtures with potassium chlorate;mixtures of lead sulfocyanate with potassium chlorate and iinely groundsmokeless powder or sulfur lor calcium silicide; a complex lead salt oflead nitrate with a bis basic lead salt of a nitrophenol (U. S.2,175,249) or` mixtures of'such a salt with lead azide, with leadsulfocyanate, with potassium chlorate, or with potassium chlorate andinely ground smokeless powder; lead styphnate or its mixtures withtetryl; diazodinitrophenol or its mixtures with potassium chlorate; leadazide; mixtures of bismuth and selenium with a small amount of potassiumchlorate; mixtures of boron and red lead; tetrazene or its mixtures withnely ground smokeless powder, or with aluminum and nitromannitol; andmany others.

These ignition compositions are used in our pressureresponsivedetonator, wherein no electric connections nor bridge wire are present,in loose, granular form, i. e. without compression and without the useof a binder. In this condition they are essentially free-owing. Theignition composition is introduced into its portion of the detonatorshell in such quantity that a considerable majority of the chamber whichit occupies is free air space. The free airspace, which air spaceincludes the total volume of; the voids between the particles, is equalto 70-85% of the volume of the collapse chamber. Whenpressure-responsive delay detonators are used, it is preferable that the'ignition composition be one that produces little or no gas Von burning,e. g. a mixture of boron and red lead or a mixture of bismuth andselenium with a small percentage, no more than about 5%, ofl potassiumchlorate.

The wall of the detonator according to the invention may be made of anysuitable metal such as gilding metal, brass, aluminum, copper or steel.The walls will desirably be of somewhat greater strength than those ofordinary detonators. In any event, the walls should be of such strengththat the tubular container will withstand static pressures of more than2000 lb./sq. in. in that portion containing the ignition composition.VIf Vthe walls are of lesser strength, the hazard exists of theaccidental detonation ofl the detonator by unintentional squeezing, asby being stepped on, for example. In many cases, even greater Wallstrengths are desirable. For example, when the pressure-responsivedetonators are to be used in deep oil wells where high hydrostaticpressures are to be expected, it may be necessary to provide shellshaving wall strengths which will withstand pressures greater than 10,0001b./sq. in. before collapse occurs.

When wall strengths which will withstand high pressures such as thosegreater than 10,000 lb./sq. in. are used, the eventual collapse, understill higher pressures, of the detonator in the portion loosely lled bythe ignition composition is of such force that the ignition compositionis fired with certainty. When, however, wall strengths in the Vicinityof those which will withstand static pressures of about 2500 lb./sq. in.are used, it is often desirable to include in the collapse chamber atleast one solid, non-reacting hard object of 'irregular shape, whichmay, for convenience, be designated as an anvil, in order to provide afriction surface which will facilitate ignition of the ignitioncomposition upon collapse of the shell wall. Such an object has beenshown in the bent wire 6 of Figure 2. Other elongated wires or rods ofirregular shape, e. g. serrated rods, may also be used. When large,rigid objects of the type of wires are introduced, it is desirable forthe sake of safety that they be fastened in position Within the collapsechamber. For example, they may be inserted in the closing plug of thedetonator shell, as illustrated in Figure 2. Other, smaller hard objectsof irregular shape may also be introduced into the collapse chamberalong with the ignition composition. For example, it may be desirable tointroduce grains of sand or quartz to insure adequate friction surfacein detonators having walls of the lower strengths, i. e. thoseapproaching the lower limit of 2000 lb./ sq. in. It will be understoodthat suitable adjustments `may be made in wall strength, choice ofignition composition, amount of space in the collapse chamber lled bythe ignition composition, and inclusion or not of an anvil to t thedetonator to its particular conditions of use.

For example, ,a satisfactory pressure-responsive detonator for use at acollapse pressure of about 2500 lb./sq. in. may be prepared by pressinga base charge of cyclotrimethylenetrinitramine into a gilding metalshell of the type shown in Figure 2 of a diameter of 0.279 in. and awall thickness of 0.009 in. A priming or intermediate charge of leadazide is loaded at a pressure of 4000 lb./sq. in. into the cavity in thebase charge. Above this charge a section of the tubular shell 1 in. indepth is lled to a depth of about 1/2 in. with a loose, granular mixtureof 50 parts by wegiht lead sulfocyanate, 40 parts potassium chlorate,and 10 parts sulfur. The one-inch section of tube is closed by a rubberplug containing a waved Wire anvil such as is illustrated at 6 in Figure2, which plug is crimped tightly in place. The one-inch sectioncontaining the loose, granular charge to one-half its depth thus has nointernal support, in contrast to those portions of the. detonatorcontaining the pressedv charges and the closing plug. When a detonatorconstructed and loaded in this manner is subjected to test by beingintroduced into a heavy-walled pipe lled with a liquid the hydrostaticpressure of which is increased by means of a pump until the detonator-collapses and detonates, -it is found-that the collapse occurs at about2500 lb./sq. in. `When such detonators yare used-in an'underwaterblasting assembly such as is shown in Figure 7, for example, all theexplosive charges containingthese detonators are exploded by the suddenincrease in pressure brought about by the detonation of an explosivecharge under water vin -their vicinity.

For a pressure-responsive detonator to be used at'higher pressures,about 12,000 lb./sq. in.,'for example, a tube such asis shown in Figure4 0f gilding metal about 0.311 in. in diameter and of 0.025 in. wallthickness is provided with a closing plug 9 at one end. A base charge ofpressed cyclotrimethylenetrinitramine and an intermediate charge of leadazide pressed at 4000 lb./sq. in. are introduced into the -bottom of theclosed tube. Into a space within'the tube about'l in.'in depth isintroduced to a depth of kabout 1/2 in. a loose, granular ignitioncharge comprisingamixture of 50% by weight of ground smokeless powder,25% of a complex salt of lead nitrate with a bis basic lead salt of4,6-'dinitroortho-cresol, and' 25% of potassium chlorate. The one inchsection of tube is closed by a second plug 9. No anvil is required inthe ydetonator here described because the detonator is constructed tocollapse at the internally unsupported portion at such highpressure thatcollapse, when it does occur, is so sudden and energetic that anadditional friction-promoting element is superfluous. When adetonator-constructed and loaded in this manner is subjected to testby'being introduced into a heavy-walled pipe filled with -a liquid thehydrostatic pressure of which is increasediby means of a pump until thedetonator collapses and detonates, itis found thatV the collapse occursat about 12,000 1b./'sq. in. When such detonators are used in a blastingassembly such as is shown in Figure 8, for example, at the bottom of adeep oil well, where high hydrostatic pressure exists, they resistcollapse at the high hy drostatic pressures in the well, but thepressure-responsive detonators'in the assembly, and consequently theexplosive charges, are exploded by the sudden increase in pressurebrought about by the detonation of an explosive charge in the liquidmedium of the well in their vicinity.

It is'believed that the functioning of our detonator depends on thepinching of the ignition composition in thin layers between the folds ofthe suddenly collapsing metal Walls or between the wall and the anviland that the heat generated thereby initiates the ignitioncompositiomwhich, in its turn, starts the intermediate charge or thedelay charge, if Va delay charge is present, and that the large amountof free air space is necessary to permit the free movement of the owablegranular solid ignition composition. When an ignition composition ispacked tightly, ignition is likely not to occur. Although the variousignition compositions vary in specific gravity and Igrain size,-withconsequent variation in the volume ofthe voidsbetween the 'solidparticles, we ordinarily prefer to vll the unsupported"collapse chamberto about one-halfwith the ignition composition, on a bulk basis. Theremaining half of free air space combined with the volume of voidsbetween the solids provides a large amount of space within which theignition composition can-move. 1We have found that when the combined airspace plus the voids is equal to 70-85% of the volume of -the chambersatisfactory ignition occurs. When the total air space is greater than85%, there may be too little of -the ignition composition present toassure ignition, and when the total air space is less than 70% it ispossible Ythat suflicient'frictional compression of the ignitioncomposition will not take place.

Furthermore, in order to `assure collapse of the shell inthe' internallyunsupported portion containing the loose, granularignition compositionto a degree to bringmetal 'surfaces in contact, it's necessary that thisinternally un- -eter of the shell.

It .will be Iunderstood that the pressure-responsive detonators of thepresent invention difer from the percussion caps which have been used inmilitary explosives in that no percussion pin or other object isrequired to come into contact with the detonator. In fact, such anobject would indent the detonator to such an extent as to cause internalmetal-to-metal contact only with dilficulty'because of the strength ofthe shell wall. If, on the other hand, an object were to penetrate theshell wall, liquid would enter, and the detonator would fail tofunction. Furthermore, either indentation or penetration would beunlikely to find sufficient explosive composition at the point ofpercussion to become ignited because of the free space within thecollapse chamber and the freely llowing nature of the loose, granularignition composition. v

Whereas examples have been given of various diameters and wallthicknesses of the detonator shell, these are not limiting because oneskilled in the art can readily determine the diameter and the wallthickness required for any particular metal to attain the collapsestrength desired, which strength may be tested by controlled hydrostaticcollapse of the shell in the absence of the ignition composition.

It is essential that the shell be sealed tightly, and the seal willdesirably be such as to be maintained under considerable pressure. Thesealing means shown in Figures 1-4 are effective means for achievingclosures which are resistant to high pressures. Other means may also beused. It may, however, be desirable to seal the shell in such mannerthat the sealing means will be resistant to the pressure of thesurrounding medium but will give Way under the pressure developed bythe-explosive chargered in the vicinity of the propagation detonatorsand be instrumental in effecting ignition. When so used, the sealingmeans will desirably be coated or tipped with metal on the inner side.It will be understood that such an arrangement comes within the scope ofthe invention.

The method of underwater blasting according to the present invention isoutstanding in its advantages. The pressure-responsive detonators usedare simpler indesign and more economical in cost of materials thanelectric blasting caps. Since only one electric blasting cap is requiredfor a group of shots, this means a very considerable savings,particularly in cap wires and electrical firing means. At the same timethe disadvantages are avoided of a large number of sets of cap wiresthat may become fouled by floating or submerged objects and mayconstitute'a hazard during the occurrence of electrical storms, even ata considerable distance from the place of blasting.

A particular advantage comes from the fact that the method allows thesatisfactory and 'elfective use ofi-explosives of a lower order ofsensitivity than has been possible heretofore in the usual proceduresfollowed. It has previously been the practice in submarine blasting toemploy 60% straight dynamite, in order to assure complete detonationwhere propagation from hole to hole was desired. This 60% straightdynamite is of a high degree of sensitivity, and its use in large-scaleblasting operations is not desirable because of the'rough treatmentinvolved, and the care -required in -such handling. By using the methodof the present invention, any cap-sensitive explosive may be employed,and We iind highly desirable explosives relatively insensitive to impactsuch as those high in ammonium nitrate .content, for instance over 60%ammonium nitrate, nonnitroglycerin explosives containing solidsensitizers, granulated cast mixtures of ammonium vnitrate .andtrinitrotoluene, blasting agents of the llNlitramon type where aicap-sensitive "booster charge is ,re quired, and many others. With suchexplosives -l'lav-l ing a pressure-responsive detonator inserted in eachcartridge or in veach group of-cartridges, the advantages are obtainedof excellent blasting execution, simplicity of assembly, and freedomfrom the hazards of sensitive explosives. It will be `understood that,when the term explosive charge is used, this may designate either asingle explosive cartridge or a group of cartridges in substantialcontact or in detonating relationship with one another.

The invention has been disclosed at length in foregoing, but it will beunderstood that many changes in details of charges, arrangement ofcharges, assembly and detonator design may be made without departurefrom the scope of the invention.

' We intend to be limited, therefore, only by the following claims.

We claim:

1. A detonator for use in blasting operations in contact with a denseliquid medium and adapted to b e initiated by pressure resulting from anearby explosion, said detonator comprising a completely sealed tubularmetal shell containing a base charge of a dense, highvelocity explosive,a compressed priming charge, and, in a portion of the shell in ignitionrelationship with the priming charge, said portion being at least twiceas long as the diameter of the shell, a loose, granular ignitioncomposition susceptible to ignition by an incandescent wire, thecombined air space plus the voids within said portion amounting to70-85% of the volume of said portion, the.walls of said shell being of astrength such as to undergo substantial collapse at static pressuresgreater than 2000 lb./sq. in., whereby the shell wall is collapsed underthe effect of pressures greater than 2000 lb./sq. in. transmittedthrough a dense liquid medium and wherein the ignition of the looseignition composition is produced by such wall collapse.

2. A detonator in accordance with claim l, in which at least one solid,nonreacting hard object of irregular shape is present in the portion ofthe shell containing the loose, granular ignition composition.

3. A detonator in accordance with claim l, wherein the shell Wall is ofa strength such as to undergo substantial collapse at pressures greaterthan 10,000 lb./sq. in.

4. A delay detonator for use in blasting operations in contact with adense liquid medium and adapted to be initiated by pressure resultingfrom a nearby explosion, said delay detonator comprising a completelysealed tubular metal shell containing a base charge of a dense,high-velocity explosive, a compressed priming charge, a delay charge inignition relationship with the priming charge, and, in a chambercontiguous to the delay charge, said chamber being at least twice aslong as the diameter of the shell, a loose, granular explosivecomposition susceptible to ignition by an incandescent wire and whichproduces little or no gas on burning, the combined air space plus thevoids within said chamber amounting to 70-85% of the volume of thechamber, the walls of said shell being of a strength such as to undergosubstantial collapse at static pressures greater than 2000 lb./sq. in.,whereby the shell wall is collapsed in liquid media under the effect ofpressures greater than 2000 lb./sq. in. and wherein the ignition of theloose, ignition-type explosive composition is produced by such wallcollapse.

5. A detonator for use in blasting operations incontact with a denseliquid medium and adapted to be initiated by pressure resulting from anearby explosion, said detonator comprising, in a metal shell closed atone end and of a strength such as to undergo substantial collapse atstatic pressures greater than 2000 lb./sq. in., a high-density basecharge, a compressed priming charge, and, in a chamber between thepriming charge and a plug sealing the top of the shell in a water-tightmanner, said chamber being not less in length than twice the diameter ofthe shell, a loose, granular explosive composition capable of ignitionby an incandescent wire, the combined air space plus the voids withinsaid chamber amounting to 70-85% of the volume of the chamber,

whereby the detonator s initiated in liquid media by pressures greaterthan 2000 lb./sq. in. acting on the shellof the detonator.

6. A detonator for use inblasting operations in contact with a denseliquid medium and adapted to be initiated by pressure resulting from anearby explosion, said detonator comprising, in a metal shell closed atone end, a dense, high-velocity base charge, a compressed primingcharge, and, in a chamber between the priming charge and a plug sealingthe top of the shell in a watertight manner, said chamber being at leastas long as twice the diameter of the shell and containing at least onesolid, nonreacting hard object of irregular shape, a loose, granularignition composition susceptible to ignition by an incandescent wire,the combined air space plus the voids within said chamber amounting to 70-85% of the volume of the chamber, the walls of said shell being of astrength such as to undergo substantial collapse at static pressures ofabout 2500 lb./sq. in.

7. A detonator for use in blasting operations in contact with a denseliquid medium and adapted to be initiated by pressure resulting from anearby explosion, said detonator comprising, in a completely sealedmetal shell, a high-density, high-velocity base charge, a compressedpriming charge, and, in a portion of the shell in ignition relationshipwith the priming charge, said portion being at least twice as long asthe diameter of the shell, a loose, granular ignition compositionsusceptible to ignition by an incandescent wire, the combined air spaceplus the voids within said portion amounting to 70-85% of the volume ofsaid portion, the walls of said shell being of a strengthsuch as toundergo substantial collapse at static pressures of about 12,000 lb./sq.in.

8. A detonator for use in blasting operations in contact with a denseliquid medium and adapted to be initiated by pressure resulting from anearby explosion, said detonator comprising a completely sealed tubularshell of a metal selected from the group consisting of gilding metal,brass, aluminum, copper, and steel, said shell containing a base chargeof a dense high-velocity explosive, a compressed priming charge, and, ina portion of the shell in ignition relationship with the priming charge,said portion being at least twice as long as the diameter of the shell,a loose, granular ignition composition susceptible to ignition by anincandescent wire, the combined air space plus the voids within saidportion amounting to 70 to 85% of the volume of said portion, the wallsof said shell being of a strength such as to undergo substantialcollapse at static pressures greater than 2000 lb./sq. in., whereby theshell wall is collapsed under the etect of pressures greater than 2000lb./ sq. in. transmitted through a dense liquid medium, and wherein theignition of the loose, granular ignition composition is produced by suchshell collapse.

9. A detonator for use in blasting operations in contact with a denseliquid medium and adapted to be initiated by pressure resulting from anearby explosion, said detonator comprising a completely sealed tubularmetal shell containing a base charge of a dense, high-velocityexplosive, a compressed priming charge, and, in a portion of the shellin ignition relationship with the priming charge, said portion being atleast twice as long as the diameter of the shell, a loose, granularignition composition selected from the group consisting of mercuryfulminate alone and with potassium chlorate; lead sulfocyanate-potassiumchlorate mixtures (l) with smokeless powder, (2) with sulfur, and (3)with calcium silicide; a complex lead salt of lead nitrate with a bisbasic lead salt of a nitrophenol (l) alone, (2) with lead azide, (3)with lead sulfocyanate, (4) with potassium chlorate, and (5) withpotassium chlorate and smokeless powder; lead styphnate alone and withtetryl; diazodinitrophenol alone and with potassium chlorate; leadazide; mixtures of bismuth and selenium with potassium chlorate;mixtures of boron and red lead; tetrazine (l) alone, (2) withsmokeemessa lessk powder, (3)with-aluminum, and (4) with nitromam nitol;the combined air spaceplus the yvoidswithin said portion amounting to 70to 85% of the volume-of said portion, the Walls of said'shellbeing ofastrength such as to undergo substantial collapse at staticpressures'greater than 2000 lb./sq. in., whereby the shell wall is c01-Vlapsed under the effect of pressures greater :than 2000 lb./sq. in.transmitted through a dense `liquid medium and wherein'the ignitionof-the loose ignition composition is produced by such wall collapse.

10. A detonator for use in blasting'operations in contact with adenseliquicl medium and adapted to be initiated by pressure resultingfrom a nearby explosion, Said cletonator comprising a completely sealedtubular metal shell containing a lbase chai-geef a dense, high-velocityexplosive, a compressed priming-charge, and, ina portion of the shell inignition relationship with the priming charge, said portion being atleast twice as long as the diameter of the shell, a loose, granularignition composition, thecombined air space plus the voids within saidportion amounting to 70 to 85% of the volumeof said portion, the Wallsof said shell being of a strength 'at least of the order of magnitude ofthat of a gilding metal shell having afwall thickness of 0.025 inch, soas to undergosubstantial collapse at selected static pressures greaterthan 2000 lb./ sq. in., whereby the shell Wall is not collapsed'below2000 lb./sq. in. but is collapsed under the effect of selected pressuresgreater than 2000 lb./sq. in. transmitted through a dense liquid mediumand wherein the ignition of the loose ignition composition is producedby such Wall collapse.

References Cited in the le of this patent UNITED STATES PATENTS1,968,134 Eschbach et al July 31, 1.934 2,139,581 Hanley Dec. 6, 19382,420,651 Burrows May 20, 1947

1. A DETONATOR FOR USE IN BLASTING OPERATIONS IN CONTACT WITH A DENSELIQUID MEDIUM AND ADAPTED TO BE INITIATED BY PRESSURE RESULTING FROM ANEARBY EXPLOSION, SAID DETONATOR COMPRISING A COMPLETELY SEALED TUBULARMETAL SHELL CONTAINING A BASE CHARGE OF A DENSE, HIGHVELOCITY EXPLOSIVE,A COMPRESSED PRIMING CHARGE, AND, IN A PORTION OF THE SHELL IN IGNITIONRELATIONSHIP WITH THE PRIMING CHARGE, SAID PORTION BEING AT LEAST TWICEAS LONG AS THE DIAMETER OF THE SHELL, A LOOSE, GRANULAR IGNITIONCOMPOSITION SUSCEPTIBLE TO IGNITION BY AN INCANDESCENT WIRE, THECOMBINED AIR SPACE PLUS THE VOIDS WITHIN SAID PORTION AMOUNTING TO70-85% OF THE VOLUME OF SAID PORTION, THE WALLS OF SAID SHELL BEING OF ASTRENGTH SUCH AS TO UNDERGO SUBSTANTIAL COLLAPSE AT STATIC PRESSURESGREATER THAN 2000 LB./SQ. IN., WHEREBY THE SHELL WALL IS COLLAPSED UNDERTHE EFFECT OF PRESSURES GREATER THAN 2000 LB./SQ. IN. TRANSMITTEDTHROUGH A DENSE LIQUID MEDIUM AND WHEREIN THE IGNITION OF THE LOOSEIGNITION COMPOSITION IS PRODUCED BY SUCH WALL COLLAPSE.